Sounds and Noises
Different Sounds from the Outdoor Unit
Compressor
All the two stage units will start in low stage and can then move into second stage based on a thermostat demand.
Noises associated with the compressor can be at start, while running in either stage, or at shut down. It's important to pick up on when the noise is present so you can properly address the issue.
If, for instance, you have a loud start up noise, it could very well be because liquid has migrated into the compressor in the off cycle. In this case look for a crankcase heater and verify it is working in the off cycle. Short cycling may be a problem as well because the crankcase heater doesn't have time to warm the compressor. Most compressor noises are related to liquid refrigerant or charge issues.
Cabinet
A cabinet that is in a bind can exaggerate normal vibrations. Systems are designed to avoid certain frequencies and when the cabinet or tubing is altered, it may impact the design. It can then appear to be a fan blade out of balance, but it may not actually be the case. For instance if a unit is set on a warped pad and the weight of the unit is not equal on each of the 4 corners, it can put a very small twist in the cabinet. If when removing a panel, you notice a slight shift in the remaining cabinet panels, this would indicate a cabinet that is in a bind. Try adjusting the way each corner lands on the pad with shims.
Fan Blade
This is almost always the first go to for most technicians. Why would a fan blade suddenly become out of balance? Well there are a number of reasons. Its rare, but it could have thrown a weight. Look at the stopped blade for any indication that a weight was present but is no more. Almost certainly, if it through one, its in the bottom of the cabinet somewhere. Another thing to look at is signs of damage. A bent blade can be a source of vibration as well. You may have to replace a blade that has been damaged, but don't stop there... What caused it? Look above the unit. Is it possible icicles or large volumes of water are coming off the roof into the unit whether its running or not? Finally check the blades at the spider. Make sure the connection is firm, loose rivets or welds can cause a fan to be noisy and eventually break. The last thing we want is a fan spinning at a high RPM to come apart. Nothing good can come from that.
